Pneumatic valve actuators to open and close gate valves for allowing or prohibiting flow in a flowline are well known. Generally, such actuators are operated by applying a pneumatic force to a diaphragm which diaphragm acts on a valve stem to maintain the gate valve in an open position so as to allow fluid or gas to pass therethrough. Under conditions such as emergency conditions where leaks from the flowline may occur or if the fluid input to the flowline exceeds its output, the air holding the actuator in the open position is exhausted from the actuator and a preloaded compression spring forces the valve stem of the actuator to move so that as to close the valve in a fail-safe type configuration.
Pneumatic valve actuators of the type referred to, however, suffer from disadvantages. One disadvantage lies in the removal of the actuator from the attachment flange to which the actuator is connected. In previous actuators and in order to repair the actuator, the actuator had to be removed from the valve stem of the shut-in valve. In many instances, it could not be so removed unless the shut-in valve was disassembled and the flow through the flowline terminated.